I am a SEO, I can confirm u the drop in the ranking is bcoz of panda update
< cough >
On a serious note, I would echo the advice to get at least one good pair of eyes on your site. And if you feel you've possibly been burnt by one provider, then a community review by knowledgable webmasters could well be the best initial option.
The drop seems a little bit sudden to be any links having been removed. Could just be bad timing. But you have to bear in mind that your site does not exist in isolation. Your page 1 result consists of your site and others too.
So, did the other sites change things? Did their links change? Did Google change the way it sees you - or your competitors?
There are lots of factors that go into building the top ten results for any phrase, and you also have to factor personalisation into it. What you see may well be very different from what others see.
Do your web stats show any significant or out of character changes?